The present invention relates to high speed switching technologies for a fail-over, especially to a high speed switching technology for a disk image delivery system fail-over.
In a computer system attached to a SAN (Storage Attached Network), it is possible to change computers accessible to a particular LU (Logical Unit) with each other by changing the security settings for the LU in a storage subsystem attached to the SAN and for HBAs (Host Bus Adapters) integrated in the computers. Using this approach, a fail-over method, where a computer is changed to another one without changing LUs when the former computer breaks down, has been realized. Another fail-over method which achieves a similar effect by changing the WWNs (World Wide Names) of HBAs without changing the security settings has been realized. Both fail-over methods need expensive storage devices while being capable of providing high speed fail-over functions.
Therefore, there is a high demand for more inexpensive fail-over methods. Compared with the above mentioned fail-over methods, another method, where the disk image of the failed computer is delivered to a spare computer, has been proposed as an inexpensive fail-over method (JP-A-2006-11781). Because this disk image delivery method does not need expensive storage devices, it is possible to build an inexpensive system with high availability. However, there is a problem in that it takes time to complete the fail-over because the delivery starts after a failure occurs.